This invention relates to a printer and printing control method and, more particularly, to a printer and printing control method for performing printing using a printhead, utilizing an ink-jet printing method by discharging ink on a printing medium.
A printer for performing printing in accordance with the ink-jet printing method has a printhead, which discharges ink droplets, and an ink tank which supplies ink to the printhead.
The basic operation of the printhead is explained below with reference to FIG. 5.
FIG. 5 is a schematic view showing a configuration of a part of an ink discharge portion of a printhead 9.
Referring to FIG. 5, the printhead 9 which faces to a printing medium 1, such as a recording paper sheet, includes a plurality of ink discharge orifices 10 formed at predetermined intervals in the vertical direction. When printing, each of the electrothermal transducers 11 (e.g., heating resistor) arranged in correspondence with the respective ink discharge orifices 10 is driven (heated by sending electric current) in accordance with inputted printing information, thereby causing ink film boiling, and consequently a bubble 12 is formed in the ink. The pressure of the formed bubble 12 causes ink to be discharged from the ink discharge orifice 10. An ink droplet 13A formed in the ink discharge operation adheres to the printing medium 1, and a predetermined pattern is formed, thereby printing is performed in a dot pattern. Note that the electrothermal transducers 11 (e.g., heating resistor) are applied with a heat voltage (VH) controlled external to the printhead.
Thereafter, when the driving of the electrothermal transducers 11 is stopped, the inside of nozzles 11A of the printhead 9 gradually cools down, and the bubble 12 disappears.
The printhead 9 is equipped with a heat driver 14 for switching on/off electric current to the electrothermal transducers 11, a serial/parallel converter 16 for temporarily storing serially inputted printing information and converting it into parallel data, and a heat signal generator 17 for providing a heat signal to the heat driver 14. Further, a circuit substrate of a printhead controller 29 for providing print data to the serial/parallel converter 16 in synchronization with a clock signal and providing a heat signal to the heat signal generator 17 is installed in a carriage on which the printhead 9 is mounted.
Further, in FIG. 5, reference numeral 10A denotes a common liquid chamber for ink connected to the respective nozzles 11A, and reference numeral 13 denotes a liquid channel from an ink tank to the common liquid chamber 10A.
Next, a conventional row-column conversion will be explained with reference to FIG. 6.
Conventionally, data transmitted from a host computer (referred to as "host" hereinafter) to a printer is divided by n bits (generally, n=8) in the direction perpendicular to the conveyance direction of the printing medium 1 as shown in FIG. 6A. Such data is stored in a receiving buffer 25a provided in RAM 25 of the printer in the received order as shown in FIG. 6B.
The nozzles of the printhead 9 are arranged in the direction parallel to the conveyance direction of the printing medium 1. Therefore, as shown in FIG. 6B, when transmitting the data temporarily stored in the receiving buffer 25a to a print buffer 25b, the data is transmitted by an amount corresponding to n.times.N-bit addresses at predetermined intervals, thereby divided into blocks of n.times.n bits. Then, each block of the divided data is rotated 90 degrees in a data processor 102. The above processing is called row-column conversion or H(honrizontal)-V(vertical) conversion (hereinafter referred to as "R-C conversion").
Then, the R-C converted data is transmitted to the printhead 9 in corresponding to the number of nozzles of the printhead via the printhead controller 29.
Next, a conventional smoothing processing will be explained with reference to FIG. 7.
Recently, the resolution of a printer has been increased to improve the quality of a printed image. However, the resolution of data transmitted from a host to the printer is sometimes lower than that of the printer. In such cases, the resolution of print data may be converted to the resolution of the printer in the printer.
For instance, print data which represents a character pattern 701 as shown in FIG. 7 with a resolution of m.times.m dots per unit area (8.times.8 dots in 702 of FIG. 7) is converted into a resolution of 2m.times.2m dots per unit area (16.times.16 dots in 703 of FIG. 7). However, if the resolution conversion of the print data is simply performed as in the manner shown in 703 of FIG. 7, the quality of a printed image remains the same as that of the print data of the original resolution.
One purpose of representing an image in high resolution is to print smooth curves and smooth slanting lines; therefore, after a resolution of the print data is converted, the print data is further corrected in the printer as shown in 704 of FIG. 7 so as to obtain smooth curves and smooth slanting lines. The above operation is called smoothing.
The simplest smoothing processing is to divide data in the print buffer 25b into blocks of i.times.j bits, compare them to patterns of i.times.j bits prestored in ROM, and apply predetermined corrections to the divided data if the divided data matches one of the patterns. Thus, in the smoothing processing, processes of comparison and correction are repeatedly performed for each of the plurality of patterns.
In the above conventional embodiment, however, when resolution conversion is performed, the print data is unconditionally subjected to smoothing processing; therefore, it takes a considerable time to perform smoothing processing, thus resulting in decreasing of throughput of the printer.
Taking into consideration that an increase in throughput of a printer is highly required as performance and processing speed of a host improve, low throughput of a printer is a considerable problem.